Gazing down along The Mall, all they could see was a tide of humanity ebbing and flowing in waves of euphoria.
The two young princesses, Elizabeth and Margaret Rose, had known for some time that this moment was coming and that victory in Europe was assured.
But, as they joined the King and Queen on the balcony of Buckingham Palace on VE Day in 1945, the sheltered young royals were unprepared for the electric atmosphere and sense of release bubbling from the crowds.
They were desperate to be part of it.
A few hours later, Lilibet, 19, and her 14-year-old sister sneaked out of the palace with the blessing of their parents, who agreed “the poor darlings” deserved a little fun at last.
Then, going almost unrecognised, they found themselves dancing with strangers, joining a rowdy conga and cheering up at their waving parents as they appeared again on the balcony.
“I think it was one of the most memorable moments of my life,” the Queen would recall in a rare and candid TV interview in 1985.
“I remember lines of unknown people linking arms and walking down Whitehall, all of us just swept along on a tide of happiness and relief.”
The Queen will share her memories in a VE Day 75th anniversary address at 9pm today – the same time her father spoke to the nation in 1945.
Earlier in the day, Prince Charles will read extracts from his grandfather George VI’s diary.
King George VI and Queen Elizabeth had steadfastly refused to leave London during the war, despite an extremely near miss when the Luftwaffe pulverised the Buckingham Palace Chapel in September 1940.
The princesses remained at Windsor Castle and their parents joined them a few days before, knowing victory was imminent.
The King had been working on his victory address with voice coach Lionel Logue, who had helped him overcome his stammer (as depicted in the 2010 movie The King’s Speech.)
On Monday, May 7, the royals returned to Buckingham Palace as it was announced that Tuesday and Wednesday would be VE Day public holidays.
Huge crowds began descending on London overnight, awaiting Prime Minister Winston Churchill’s announcement the following afternoon.
The King wrote in his diary: “The day we have been longing for has arrived at last and we can look back with thankfulness to God that our tribulation is over.”
Loudspeakers and floodlights were being erected in The Mall and the palace balcony – newly strengthened after the bombings – was decorated with crimson and gold drapes.
Princess Elizabeth, a mechanic and driver in the Auxiliary Territorial Service, dressed in her uniform while Princess Margaret wore a light-coloured jacket and skirt.
Then, after a morning of tense anticipation, the royals listened to Mr Churchill’s 3pm speech from Downing Street.
They could hear the crowds going wild outside as Churchill ended with the words: “Advance Britannia! Long live the cause of freedom! God Save the King!”
And then they made the first of many balcony appearances that day, including one with Churchill himself.
Lionel Logue and his wife, Myrtle, arrived at the palace to dine with the royals before Logue gave the King’s speech a final run-through.
By now the princesses were pleading with their parents to be allowed to join the party.
Finally, they agreed to let them leave in a group of 16, including some guards officers, the Queen’s cousin, the Hon Margaret Rhodes, and lady-in-waiting Jean Woodroffe. They were also joined by Lord “Porchy” Porchester, who later become the Queen’s racing manager, and Peter Townsend, the king’s equerry who sparked a national crisis a decade later when, though a divorced man, he won Princess Margaret’s heart.
Speaking in 2015, Margaret Rhodes revealed: “We crossed the forecourt at Buckingham Palace and got to the railings and there were these masses and masses of people. There was a general thing of, ‘We want the King and Queen!’ which we all frantically joined in with.
“We were amazed when, five or 10 minutes later, the windows opened and they came out on to the balcony.
“It was like a wonderful escape for the girls. I don’t think they’d ever been out among millions of people.”
In 1985 the Queen herself revealed: “We were terrified of being recognised, so I pulled my uniform cap well down over my eyes.
“But a Grenadier officer among our party… said he refused to be seen in the company of another officer improperly dressed – so I had to put my cap on normally.”
The Queen was recognised by at least one eagle-eyed member of the crowd though – a teenage lad who stole a dance.
Ronald Thomas’s story only emerged in 2015 when the partially fictionalised movie A Royal Night Out featured a similar incident
Ronald, then 15, from Harrow, had travelled to London with a pal.
In Trafalgar Square, he recognised Elizabeth.
His grandson Thomas, 33, explained: “They danced together for a few minutes – just a merry dance.
“She denied her identity at first but he was so sure, he said, ‘I’d recognise your face anywhere!’
“Eventually she admitted it but told him to keep it quiet.
“He felt a strong sense of civic duty to the future monarch, which is why he didn’t expose her then, and why he has been very bashful about it since. “There were several big blokes with her, chaperoning, and after a few minutes they all moved on.
“He was absolutely certain it was her and I have no doubt now that his story is true.”
The Queen recalled: “I also remember when someone exchanged hats with a Dutch sailor; the poor man coming along with us in order to get his hat back.”
Margaret Rhodes said: “Trafalgar Square was jammed.
“It was a scene of joyful whoopee – full of people kissing policemen and other people. It was complete mayhem but nice mayhem.”
An hour later the princesses’ pals led them rather astray.
Margaret went on: “For some reason, we decided to go in the front door of the Ritz and do the conga. The Ritz was so stuffy and formal, we rather electrified the stuffy individuals inside. I don’t think people realised who was among the party – I think they thought it was just a group of drunk young people.
“I remember old ladies looking faintly shocked. As one congaed through, eyebrows were raised.”
Then the royal party headed home, in time to see the King and Queen emerge again on the balcony.
But, the Queen revealed: “We cheated slightly by sending a message into the house, to say we were waiting.”
Her sister Princess Margaret also remembered the scene.
She recalled: “Suddenly the lights came on and lit up the poor battle-scarred palace.”
Bringing to mind the sight of her mother dressed all in white, with a tiara sparkling in the floodlights, she added: “VE Day was a wonderful sunburst of glory.”